Baldor Bench Grinder wont get to speed

[Luc DavenportParticipant @lucdavenport26625]

I have been given a nice old Baldor bench grinder. When powered up it only runs up to 1700 rpm instead of the stated 2850. Its a nice machine and it would be great to get it running. Any thoughts? I have spoken with Baldor and they have no record of it.

[Luc DavenportParticipant @lucdavenport26625]

Bench grinder issues

[Luc DavenportParticipant @lucdavenport26625]

Plate Info

Model: G30 548 (or G3C 548)
HP: 1/4
HZ: 50
PH: 1
RPM 2840
VOLTS: 230
AMPS: 1.4
No: J1704

[not done it yetParticipant @notdoneityet]

Possibly only running on start windings? If it is, don’t do it for too long – they are not suited to extended running.

Does the speed vary cyclicly? If so the run windings may not be able to accelerate it to top speed – that could be because the start windings are switched out too early, something is tight somewhere or bearings are shot.

[Luc DavenportParticipant @lucdavenport26625]

The speed gets up to the 1700 within a few seconds and sits there happily. I was thinking it is perhaps not throwing the run winding contactor? If it has one? There are also two wires coming out of the bottom of the grinder with ceramic contact blocks on i figured these were for a capacitor but the grinder runs to the same speed with and without one.

[SillyOldDufferModerator @sillyoldduffer]

In addition to NDIY's suggestions:

That the motor starts and runs at all implies that the start Capacitor is OK

Slow running can be caused by shorted windings – if so they convert your nice old Baldor into an expensive old Baldor! Cure with new motor or a rewind ( £ ) .

Another common cause of slow running is a faulty centrifugal switch. They can fail mechanically or the contacts can stick and may be fixable. (It's a nice Baldor after all!) This photo pinched off Quora is an example of what to look for inside the motor. When the motor is spinning fast enough part marked P on the rotor operates the switch marked S. What the switch does depends on the exact type of motor you have. It might just disconnect a winding, or it might switch in a Run Capacitor. The Run capacitor (if you have one) could be faulty, an easy fix.

 

There a few guys on the forum who know far more about motors than me and their answers are worth waiting for. In the meantime are you able to put some photos up?

Dave

Edit: What I want for x-mas.  An unwanted smiley exterminator.

Edited By SillyOldDuffer on 11/12/2018 12:09:53

[Luc DavenportParticipant @lucdavenport26625]

I haven’t been near it last night ill strip the machine down tonight and see if I can get any photos.

I have thoughts about just using the casing and putting in a dc motor I have lying around if the motor is FUBAR. I certainly can’t go having it rewound.

[mechman48Participant @mechman48]

… Edit: What I want for x-mas. An unwanted smiley exterminator.

Try… if it's inside brackets / parenthesis, press space bar & leave a gap, same at end -space bar then end brackets

George.

[Les Jones 1Participant @lesjones1]

How sure are you that the tachometer reading is correct ? I would expect an induction motor running that much below design speed would get very hot..

Les.

[Luc DavenportParticipant @lucdavenport26625]

I opened the motor last night. Not good news. It appeared that the motor had been on fire at some point in its past. The lacquer on the wire was black and crumbled off with the slightest touch. I think the machine may have ground its last cutter… For now 😀

[Ian S CParticipant @iansc]

I was going to say that the start switch had stuck, and the motor as running as a 4 pole motor, you finding the windings over heated more or less confirms that.20 or 30years ago there was a story in ME by a guy who ran his pillar drill using the start windings to reduce speed, this gave him double the normal speeds. Then one sad day the magic smoke leaked out , and the motor died.

Ian S C

[Author]

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